The present invention relates to a method of preparing a foundry form by a cold set process, comprising introducing a mixture of foundry sand and a binder into a form box, covering an open end of the form box with a sealing head comprising a flexible diaphragm, and applying suction to the form box to draw the diaphragm against a surface of the mixture to compact the mixture in the form box. The invention also relates to apparatus for carrying out the method.
The invention is primarily applicable to foundry moulds, i.e. to the forms for shaping the outside of the castings. However, the invention can also be applied to the mould cores, i.e. the forms for shaping the interior of the castings, if the cores are of such a shape as the diaphragm arrangement can be used. For this reason, the unusual terms "foundry form" and "form box" are used herein to comprise both the foundry mould and mould box, and the mould core and core box. The mould box itself can contain a pattern or can have a plain bottom, e.g. contain a plain platen, to form a flat side on the casting.
The method and apparatus referred to above are described in British Patent Specification No. 1,470,672. However, it has been found that the method and apparatus can be improved for use when applying a fluid hardening medium to harden the mixture in the form box. The fluid hardening medium is usually a gas, and can act either as a catalyst or a hardening agent. The most common such process is the CO.sub.2 process in which gaseous CO.sub.2 is introduced to the form box as a hardening agent to react with a sodium silicate mixture binder. However, other processes can be used, and the invention can be applied to any chemical binder system which utilizes a fluid hardening agent. For example, with certain types of resins, a catalytic hardening agent may be in the form of an acidic gas; the acid components of the gas may be normally gases or may be normally liquid and in the form of vapours, such components including sulphurdioxide, chlorine, aluminium chloride, hydrogen chloride and hydrogen bromide.